Recently, high performance displays such as high-definition (e.g., Hi-Vision) or large-scale displays are much sought after, and various studies are performed for developing high-performance displays such as CRT displays, liquid crystal displays (LCD), and plasma display panel (PDP).
PDP is a kind of gas-discharge panel. To manufacture a PDP, two thin glass plates are disposed to face each other with partition walls (ribs) in between, and a plurality of pairs of display electrodes, a dielectric layer (typically, made of Ag or Cr/Cu/Cr in order to secure good conductivity), and a phosphor layer are formed in this order on the surface of one of the two thin glass plates facing the ribs, then the space between the two thin glass plates is filled with a discharge gas, and the space is sealed hermetically. Discharges are caused in the discharge gas to allow the phosphor to emit light. PDP has excellent characteristics. That is to say, unlike CRT, a large-screen PDP is not remarkably deep and heavy. Also, PDP does not have the problem of limited viewing angle which is observed in LCD.
Typically, the dielectric layer is made of a low-melting glass. In this case, characteristics such as enough dielectric strength, high transparency, and low baking temperature (more specifically, 600° C. or lower) are required. Glasses actually used for dielectric glass layers are lead oxide (PbO), glass (permittivity ∈=10-15) including bismuth oxide (Bi2O3), etc. (See Japanese Laid-Open Patent Application No.9-50769, for example).
Meanwhile, as it is, desired in these days that the power consumption of electrical appliances is as small as possible, it is expected that the driving power consumption will be further reduced. Especially, considering that the power consumption of PDP is increasing due to the demand for larger-screen and higher-definition displays, it is required that the power consumption is reduced more aggressively.
One method of reducing the power consumption is to reduce the permittivity ∈ in the dielectric layer. The permittivity ∈ in the dielectric layer is proportionate to the amount of electric charge accumulated in the dielectric layer. It is therefore possible to further reduce the amount of electric charge accumulated in the dielectric layer by using a dielectric layer having composition with a permittivity ∈ value lower than the PbO-base or Bi2O3-base dielectric layer. Japanese Laid-Open Patent Application No.8-77930 discloses specific glass composition with a permittivity ∈ value lower than the PbO-base or Bi2O3-base dielectric layer: Na2O—B2O3—SiO2-base glass and Na2O—B2O3—ZnO-base glass both with a permittivity ∈ value of 7.2-7.6. It is possible to reduce amount of discharge current in each pixel cell per a certain voltage applied to the plurality of pairs of display electrodes (to about half or less of conventional ones) by using glasses with the above composition. This reduces the power consumption of the PDP. Also, according to the document, the dielectric layer can be formed without using a PbO-base glass. This provides an effect of avoiding environmental pollution with Pb.
It should be noted that in actual manufacturing of a PDP using the Na2O—BO—SiO-base glass or NaO—BO—ZnO-base glass, Na2O is added to constitute more than 10 wt % of the whole dielectric layer to reduce the softening point (more specifically, to set the baking temperature to a range of 550° C. to 600° C.).
However, when the dielectric layer is made of the Na2O—B2O3—SiO2-base glass or Na2O—B2O3—ZnO-base glass, Ag and Cu contained in the display electrodes move into the dielectric layer and are deposited as colloidal particles (see Latest Plasma Display Manufacturing Technique, 1987 edition, page 234). The colloidal particles reflect visible light of a certain wavelength. This turns the color of the dielectric layer to yellow (what is called yellowing). This puts an undesired color to the light emitted from the discharge space, or reduces the amount of light to be obtained. As apparent from the above, the colloidal particles can be a cause of ill effects on display performance. When Na2O is added to constitute more than 10 wt % of the whole dielectric layer, this could also be a cause of the yellowing. For these reasons, the deposition of the colloidal particles should be avoided.
The addition of Na2O to constitute more than 10 wt % of the whole dielectric layer provides another ill effect of increasing tan δ which indicates power loss in the dielectric layer. More specifically, it decreases the dielectric strength of the dielectric layer (having thickness of 20-50 μm)to approximately 1 kV.
As described above, plasma display panels have the following three main problems currently:    1. To improve luminous efficiency by reducing the permittivity ∈ of the dielectric layer to reduce power consumption;    2. To set the softening point of the dielectric layer to a low value to ease the manufacturing process; and    3. To obtain superior display performance by preventing the yellowing of the dielectric layer to securing its transparency.
The present invention is provided to solve the above three problems and an object of the present invention to provide a PDP characterized in that the dielectric layer can be formed relatively easily, that the increase in the power consumption is restricted even if the PDP has a larger screen or higher definition, and that the PDP is driven with better luminous efficiency and display performance than conventional ones.